In recent times, haptic actuators have been widely used mainly for portable electronic devices, and provide users with various feedbacks in compliance with specific input or predetermined programs for augmented reality and enhanced user experience (UX).
For example, haptic actuators are used to generate vibrations when a mobile phone receives calls or messages, to generate haptic feedbacks when users select a menu through a keypad or touch screen, and to generate a specific haptic feedback when a game program is running.
There are many types of the aforementioned haptic actuators which are generally classified into ERMs (Eccentric Rotating Masses) generating vibration by rotating an eccentric vibration unit by a motor, LRAs (Linear Resonant Actuators) generating vibration by reciprocating a vibration unit connected to a spring by electromagnetic force, and piezoelectric actuators having piezoelectric elements. Among the aforementioned of actuators, the LRAs and the piezoelectric actuators are known faster than the ERMs in terms of response speed, and therefore generally used for providing precise haptic effects.
In addition, another type is haptic actuators which use electrostatic friction or ultrasonic surface friction.
Meanwhile, as there are various types and functions of portable electronic devices, it is a tendency that the scope of using haptic actuators is extended day by day, and the number of haptic actuators used in one electronic device is gradually increasing.
For example, the following Patent 1 discloses a wearable device for navigation to provide drivers or pedestrians with path information as a guide by installing a plurality of haptic actuators in a wrist-worn wearable device and generating various vibration patterns.
In addition, a recent active trend is to study wearable devices equipped with sensors for detecting biosignals. For example, using user's EMG (Electromyogram) signals, EEG (Electroencephalogram) signals, or EOG (Electrooculogram) signals, etc. to check user's health conditions and exercise intensities, or control operation of other electronic devices.
The following Patent 2 discloses a wrist-worn wearable device for creating control signals by using user's muscular changes following hand motions. The following Patent 3 discloses a wrist-worn wearable device for creating control signals by using motions with body vibrations and hand motions.
As described above, considering the trend that the scope of using wearable devices is gradually extended and diversified, the outlook is that the wearable devices will evolve into the direction of developing new functions or enhancing user's experience by using both sensors for detecting biosignals and haptic actuators.
In addition, another outlook is to install more haptic actuators and sensors for detecting biosignals in a wearable device to provide more various haptic effects than conventional effects.
However, since it is essential that a wearable device is small and light enough for users to feel comfortable, the size thereof is unavoidably limited. More sensors and actuators to be installed contribute to insufficient installation spaces, and significantly restrict design freedom.